The present disclosure relates to imaging systems and probes employing ultrasonic imaging transducers. The present disclosure also relates to methods of detecting changes in the angular orientation of movable elements employed for directing radiation from imaging transducers during minimally invasive imaging procedures. High resolution biomedical imaging serves numerous purposes, including assessing tissue structures and anatomy, planning and/or guiding interventions on localized regions of the body, and assessing the result of interventions that alter the structure, composition or other properties of a region.
High frequency ultrasound, in particular, has found significant use in intracardiac and intravascular applications. For these applications, ultrasound transducers are incorporated into a catheter or other device that can be inserted into a lumen or cavity within the body. Two important implementations of high frequency ultrasound are intravascular ultrasound (IVUS) for imaging blood vessels, and intracardiac echocardiography (ICE) for imaging cardiac chambers. Both ICE and IVUS are minimally invasive, and involve placing one or more ultrasound transducers inside a blood vessel or cardiac chamber to take high quality images of these structures.
Courtney et al. (US Patent Application Publication No. US20090264768) describe an intravascular/intracardiac echocardiography catheter capable of forward viewing via 3D ultrasound and/or optical imaging. This is achieved using a movable member to image at various angles. This device benefits from knowledge of the position and/or orientation of either the imaging mechanism itself or of a deflecting element, such as a mirror.
In order to correlate the images obtained using an imaging transducer with the orientation of the imaging probe, it is important to provide a mechanism for determining the relative angular orientation of the movable portion of an imaging system. This angular orientation determines an angle at which imaging energy is transmitted and/or received from the imaging probe. Courtney et al. disclose a number of angle detection mechanisms and methods. One method involves relating the rotational speed to the imaging angle, for example, using a look-up table. A series of electronic and electromechanical techniques are also described, including capacitive, resistive, electromagnetic, inductive, and strain gauge based techniques. Also described are techniques that employ diffuse scattering from a reflector using the primary imaging source. Also disclosed are optical and acoustic methods and mechanism that utilize a detection sensor that is separate from the primary imaging source to determine the imaging angle.
There are a number of limitations related to the techniques described above. For example, the use of a lookup table relating rotational speed to imaging angle may be prone to significant inaccuracy. Different orientations or situations may influence the relationship between imaging angle and rotational speeds. This may occur as a result of gravitational forces in different orientations, different temperature conditions, or stress on the catheter among others. Also, many techniques—predominantly those using modalities other than the imaging modality—may require the addition of significant complex components and energy sources.